1. Field of the Invention
The present invention relates to a thermal treatment apparatus where substrates such as semiconductor wafers are held in a substrate holder and the substrate holder is loaded into a vertical furnace where a predetermined process is carried out with respect to the substrates. Specifically, the present invention relates to a technology that is capable of reducing a period of time required to cool the substrate held in the substrate holder unloaded from the vertical furnace.
2. Description of the Related Art
A semiconductor device manufacturing apparatus includes a vertical thermal treatment apparatus where plural semiconductor wafers (referred to as wafers) are thermally treated in batch. In such a thermal treatment apparatus, the wafers stored in shelves in a wafer carrier such as a Front-Opening Unified Pod (FOUP) are transferred to a wafer boat and the wafer boat is loaded into a vertical furnace, where the substrates are concurrently thermally treated in the vertical furnace. After the thermal treatment is completed, the wafer boat is brought down from the vertical furnace, the wafers are cooled, and then the wafers are transferred back to the FOUP by a transfer robot.
At the time of unloading the wafer boat from the furnace, a temperature of the wafers is about 800° C. If the wafers at such a high temperature are transferred into the FOUP, which is made of, for example, a resin that is not tolerant to heat, may melt or cause degassing. In addition, the transfer robot may be thermally deformed. Therefore, the wafers cannot be transferred into the FOUP immediately after the wafer boat is brought down from the vertical furnace, and thus the wafers are kept at an unload position, which is below the vertical furnace, until the wafers are cooled to 70° C. or 80° C.
Patent Document 1 listed below discloses a technology that causes a clean gas to flow in a horizontal direction in the unload position below the vertical furnace, according to which the wafers located in the unload position can be cooled by the clean gas flow. In addition, Patent Document 2 discloses a cooling nozzle that blows a cooling gas to the wafer boat located in the unload position, thereby cooling the wafers. Moreover, Patent Document 3 discloses a transfer area that is enclosed by partition walls below the vertical furnace and is purged with a non-oxidizing gas such as nitrogen gas.
As the wafers become larger and the number of wafers held in the wafer boat is increased from a viewpoint of higher productivity, a thermal capacity of the wafers and the wafer boat tends to be increased. Under such circumstances, members or parts that are provided in the unload position are exposed to a large amount of heat, which may require an improved heat tolerance of the members or parts. Therefore, it is required to cool the wafers in a shorter period of time.
However, it still takes a longer time to cool the wafers according to a conventional technique for cooling the wafers and the wafer boat, and thus a longer cooling time is necessary. Therefore, it takes a long time to transfer the wafers back to the FOUP, which leads to a reduced production throughput.
Patent Document 1: Japanese Patent Application Laid-Open Publication H04-137526 (FIG. 1)
Patent Document 2: Japanese Patent Publication No. 4042812 (paragraph 0022, FIG. 4)
Patent Document 3: Japanese Patent Publication No. 3502514 (paragraph 0003)